Heyy new member and a couple questions..

Hi all, im sam and from Wiltshire, England.
Anyways, I've been thinking about building a car pc for quite a while and having thought through my choices have decided to go for a new (old) build.

I've read many posts here already, all of which were very helpful.
I have considered the following options:

-Install my amd x2 system
-Build a new mini-itx system
-Build a low power atx system

The latter is what im going for, after playing round in the psu calculator my proposed system will require 135w to power (not including the screen, but my screen is 8w)

These are the parts I've ordered:
-Amd Athlon MOBILE XP 1800+ (the mobile being important as consumes much less power, equalling less heat and less power needed)
-Asus 432 board with onboard sound and vga (able to run the mobile chip too)
-7" RCA Monitor
-Heatsink and fan compatible with board and cpu

Was gonna install a cut down version of xp and software of some sort.
Also read how someone was planning on installing a tracker ball in the centre console, i like this idea so may do that too, but for time being will use roll up silicone keyboard and usb mouse.

Does this PC sound capable of doing what i want? I know its a bit "heavy duty" for the intended use, but im planning on eventually building an atom/via epia system when funds will allow.
Just really need some advice on the power supply, was thinking M2-ATX 160w, but not certain